<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>

    <style>
        #d1{
            width: 100px;
            height: 100px;
            border: 1px solid red;
            /*margin-left: 50px;*//*左外边距*/
            /*margin-top: 100px;*//*上外边距*!*/
            /*margin: 50px ;*//*四个方向赋值*/
            /*margin: 50px 100px;*//*上下和左右赋值*/
            margin: 10px 20px 30px 40px;/*上右下左顺时针赋值*/
    }
        #d2{
            width: 100px;
            height: 100px;
            border: 1px solid blue;
            margin-top: 20px;
        }
        #s1{
            border: 1px solid blue;
            margin-left: 50px;
            margin-top: 50px;/*行内元素上下边距无效*/
        }
        #s2{
            /*左右相连彼此添加外边距相加*/
            margin-left: 30px;
        }
        #big{
            width: 200px;
            height: 200px;
            background-color: red;
            overflow:hidden;/*解决粘连问题*/
        }
        #big>div{
            width: 50px;
            height: 50px;
            background-color: green;
            margin-left: 50px;
            margin-top: 50px;  /*元素的上边缘与上级元素的上边缘重合,
            给元素添加上外边距会出现粘连问题*/
        }
        body{margin: 0;}/*去掉自带外边距*/
        /*h1{margin: 0}*/


    </style>
</head>

<body>
<h1>这是h1</h1>
<div id="big">
    <div></div>
</div>
<span id="s1">span1</span><span id="s2">span2</span>
<!--div#d1-->
<!--div.c1-->
<!--div*3-->
<div id="d1"></div>
<div id="d2"></div>
<div class="c1"></div>
<div></div>
<div></div>
<div></div>
</body>
</html>